finding the missing numbers in an array, it will format the missed numbers in range format and also it will ignore if the element is not a number

Finding the missing numbers in an array

function missingNumbers(nums) {
  var missedNums = [];
  var sortedArr = nums.sort(function(a, b) {
    return a - b;
  });
  sortedArr.forEach(function(ele, i, arr) {
    var a = +arr[i],
      b = +arr[i + 1];
    if (!b) return;
    if (isNaN(b)) {
      arr.splice(i + 1, 1);
      return;
    }
    var numGap = b - a;
    if (numGap == 2) missedNums.push(a + numGap - 1);
    if (numGap > 2) {
      var formatNum = (a + 1) + "-" + (a + numGap - 1);
      missedNums.push(formatNum);
    }
  })
  return missedNums;
}
console.log(missingNumbers([3, "num", "4", undefined, null, {a:2}, false, 7, 1, "76", 34, "23", 32, 99, 56]))